1. Field of the Invention
This invention relates generally to a graphic display in a raster-scan type video display system and more particularly to an improved method of filling a polygonal region with pixels in such a raster-scan type video display system.
2. Prior Art
A method of filling a polygonal region with pixels is disclosed, for example, in Japanese Patent Application Laid-Open No. 59-22093. In this conventional method, three refresh memories corresponding respectively to red (R), green (G) and blue (B) colors are provided as well as a working memory which provides dots corresponding to all pixels on the screen. An outline of a polygon to be displayed is described to the refresh memories, and at the same time the outline of the polygon is described to the working memory as solid lines. Then, all the dots disposed inside the outline stored to the working memory are sequentially extracted therefrom, and the dots corresponding to the extracted dots are stored to the refresh memories. According to this conventional method, even if the outline of the polygon is stored to the refresh memories as lines other than solid lines (for example, as broken lines), the interior of the outline of the polygon can be properly filled.
The above-described conventional method is, however, disadvantageous in the following respects:
(a) All of the addresses of the working memory must be accessed, so that the number of accesses becomes significantly large, which results in a loss of much time.
(b) When the polygon is of a complicated shape, it is significantly difficult to completely extract all the dots disposed inside the polygon.
(c) In the case of the polygon being a concave polygon, it is most difficult to extract all the dots inside of the polygon by one predetermined data processing. As a result, it is necessary to carry out such a data processing at least twice.
Another method using such a working memory is disclosed in Japanese Patent Application Laid-Open No. 59-15289. Still another method which does not use such a working memory is disclosed in Japanese Patent Application Laid-Open No. 57-101886. However, these methods are also disadvantageous in that the number of vertices of the polygon is limited, that the kind of the outline or boundary of the polygon is restricted to certain ones, and that a large number of calculations must be performed.